The objectives of the proposed research are: (1) to develop further DMOD, a mathematical model of the role of aversive nonreward in simple and complex appetitive learning situations including the preference for predictable events (observing response acquisition); (2) to determine additional variables which influence the observing response; and (3) to retest the effect of certain variables which have been tested in uncontrolled experimental paradigms only. The model which I have developed is based on the Rescorla-Wagner model, but assumes that both larger and smaller than expected rewards are surprising and are the basis of conditioning. It predicts acquisition of the observing response because signalled nonreward is less aversive than unsignalled nonreward. If correct, the implication is clear: transform unpredictable situations into predictable ones to reduce aversiveness of situations where nonreward or failure is unavoidable.